1. Field of Invention
The present invention relates to an optical proximity correction process. More particularly, the present invention relates to an optical proximity correction process implementing an interpolation for designing a layout of a mask.
2. Description of Related Art
Nowadays, with the development of the integrated circuit (IC), element downsizing and integration is an essential trend, and is also an important topic for each industry to actively develop. In the whole semiconductor process, lithography may be referred to as one of the most important steps. Therefore, the fidelity of transferring the photomask pattern to the wafer is quite important. If the transferring of the pattern is not correct, the tolerance of the critical dimension (CD) on the chip may be affected, and the resolution of the exposure may be reduced.
The integration is gradually improved and the size of the element is gradually reduced, the distance between the elements must be reduced, therefore, in the lithography process, deviations in the transferring of the pattern may be generated, i.e. the so-called optical proximity effect (OPE). OPE may occur when the light beam is projected on the chip through the pattern on the photomask, in one aspect, the light beam is expanded due to scattering of the light beam, and in another aspect, the light beam may pass through the photoresist layer of the chip surface and may get reflected back by the semiconductive substrate of the chip.
To remedy the aforementioned deviations, a layout is often subjected to an optical proximity correction (OPC) process, which adjusts the layout to compensate for optical effects. These adjustments are made based upon results of model-based simulations of the printed layout. During the OPC process, the layout is divided into segments, such as edges, and each segment is adjusted with a negative or a positive bias. The OPC process then re-simulates the layout and measures the deviation of the resulting output pattern from the expected position, and re-adjusts the edge biases based on this deviation.
Because the segments interact with neighboring segments, any adjustments to a given segment can affect the final printed layout for neighboring segments. Hence, in an OPC process, a number of iterations of such edge adjustments are necessary for the process to converge on an acceptable result. Consequently, convergence to a final solution can require more iterations. It is important to minimize the number of the convergence iterations because performing a large number of convergence iterations takes a great deal of run time. Hence, the cost of generating the output mask pattern is increased.